The efficiency of light emitting diodes (LED) depends typically on wavelengths (green gap), junction temperature Tj and current density. An advantage of small (mini/micro) LEDs is good internal 3D-heat spreading (e.g., <60 μm diameter) and low Tj. This explains the higher efficiency at higher current density and longer device lifetime of small LEDs. For the application of even smaller μLEDs (e.g., <10 μm) like in 2D displays for augmented reality (AR) at lower drive current (e.g., 1 nA-1 μA) or 1D scanning at higher drive current (e.g., 1-300 μA) there is a different loss mechanism at different current density and size of μLEDs. For μLEDs using low current density (e.g., less than 1 uA/mm2), the efficiency can be less than 5%. In contrast, larger power LEDs can operate at up to 60% efficiency, and at medium current densities of more than 0.35 A/cm2. μLED operation may be improved by reducing non-radiative recombination in the epitaxial structure and surface recombination losses at etched mesa facets, and increasing light extraction efficiency (LEE) while operating at the low (2D display) or very high (1D-array) current density.